One of the key advantages of single-pole (SP) head/media, with a magnetically soft underlayer (SUL) and perpendicular recording system, is the capability of providing a larger write field (than that of a ring head) to enable writing into the relatively thick media with high anisotropy constant. The latter quality leads one to assume better thermal stability associated with perpendicular recording. However, this advantage is diminished as the dimension of the pole tip is reduced to increase the areal recording density [1]. So, the tradeoff between head writing field and thermal stability may still limit the achievable areal density for perpendicular recording.
FIG. 1 is a schematic representation of a typical single pole vertical recording system of the prior art. Seen there is single write pole 13 whose ABS (air bearing surface) moves parallel, and close to, the surface of recording medium 16. The latter comprises an upper, high coercivity, layer (not shown) on a magnetically soft underlayer. Coils 12 generate magnetic flux in yoke 14 which passes through main pole 14 into tip 13 and then into media 16 (where a bit is written). The magnetic circuit is completed by flux that passes through the soft under layer and then back into return pole 15. The space enclosed by the yoke and poles is normally filled with insulating material 17.
FIG. 2 is a front view of the structure shown in FIG. 1 when viewed along direction 18.
An enlarged view of the write and return poles is shown in FIG. 3. In this prior art design, the main pole 13 is about 0.1 to 0.4 microns thick at the ABS 19. The main pole is made of a high moment material, such as CoFe having a saturation magnetization, Bs, of about 2.4 T, but, in practice, this main pole does not saturate, except at the pole tip region. Thus the maximum write field in the media is mainly determined by the saturation level of the pole tip and the solid angle opened by the ABS of the pole tip.
To increase the write field, large W and t and small NH are preferred (as defined in FIGS. 1 and 2). However, for ultra-high density recording, track width W is limited by the track density requirement. To have good control of track width W, NH cannot be reduced to the extent desired due to the rounding effect of the photo mask used to pattern it. A small neck height also increases the side-fringing field and causes adjacent track erasure (ATE) [2].
A large pole width t will result in head skew problems [3]. Thus better methods for compensating field loss at ultra-high recording densities are essential. The present invention discloses a novel structure for a perpendicular write head that overcomes these problems.